Yaƙin Jena yana nufin wani gagarumin hatsaniya na soji da aka yi a ranar 14 ga Oktoba, 1806, kusa da garin Jena a jihar Thuringia, Jamus. An gwabza yakin ne tsakanin sojojin Faransa, karkashin jagorancin Napoleon Bonaparte, da kuma sojojin Prussian, karkashin jagorancin Duke Charles William Ferdinand na Brunswick. Sojojin Faransa sun yi nasara a yakin, wanda ya haifar da rugujewar ikon soja na Prussian tare da share fagen samar da kungiyar Rhine.